Common names: rhinoceros viper, river jack,^[2][3] more

Bitis nasicornis is a venomous viper species found in the forests of West and Central Africa.^[1] A big viper, it is known for its striking color pattern and prominent horns on its nose.^[3] No subspecies is recognized.^[4]

Description

Large and stout,^[5] it ranges in length from 72 cm to 107 cm.^[2] Spawls et al. (2004) mentioned a maximum length of 120 cm, but admited this is exceptional, quoting an average length of 60–90 cm.^[5] Females grow larger than males.^[6]

The head is narrow, flat, triangular and relatively small compared to the rest of the body.^[2] The neck is thin. They have a distinctive set of two or three horn-like scales on the end of their noses, the front pair of which may be quite long. The eyes are small and set well forward.^[5] The fangs are not large: rarely more than 1.5 cm in length.^[2]

Midbody there are 31-43 dorsal scale rows.^[2] These are so rough and heavily keeled that they sometimes inflict cuts on handlers when the snakes struggle.^[3] There are 117-140 ventral scales^[2] and the anal scale is single.^[5] Mallow et al. (2003) reported the subcaudals number 16-32, with males having a higher count (25-30) than females (16-19).^[2] Spawls et al. (2004) stated there are 12-32 subcaudals, paired, and males have the higher numbers of them.^[5]

The color pattern consists of a series of 15-18 blue or blue-green, oblong markings, each with a lemon-yellow line down the center. These are enclosed within irregular, black, rhombic blotches. A series of dark crimson triangles run down the flanks, narrowly bordered with green or blue. Many of the lateral scales have white tips, giving the snake a velvety appearance. The top of the head is blue or green, overlaid with a distinct black arrow mark. The belly is dull green to dirty white, strongly marbled and blotched in black and gray.^[5] Western specimens are more blue, while those from the east are more green. After they shed their skins, the bright colors fade quickly as silt from their generally moist habitat accumulates on the rough scales.^[2]

Common names

Its common names include rhinoceros viper, river jack,^[2][3] rhinoceros horned viper, riverjack,^[7] and horned puff adder.^[8]

Geographic range

Found from Guinea to Ghana in West Africa, and in Central Africa in the Central African Republic, southern Sudan, Cameroon, Gabon, Congo, DR Congo, Angola, Rwanda, Uganda and western Kenya, the type locality is listed only as "interior parts of Africa."^[1]

Habitat

This snake occurs in forested areas, rarely venturing into woodlands. Its range is therefore more restricted than B. gabonica.^[3]

Behavior

Primarily nocturnal, they hide during the day in leaf litter, in holes, around fallen trees or tangled roots of forest trees. Their vivid coloration actually gives them excellent camouflage in the dappled light conditions of the forest floor, making them almost invisible.^[2] Although mainly terrestrial, they are also known to climb into trees and thickets, where they have been found up to 3 m above the ground.^[3] This climbing behavior is aided by a partially prehensile tail.^[2] They are sometimes found in shallow pools and have been described as powerful swimmers.^[2][3]

B. nasicornis juvenile

They are slow moving, but capable of striking quickly, forwards or sideways, without coiling first or giving a warning. Holding them by the tail is not safe; as it is somewhat prehensile, they can use it to fling themselves upwards and strike.^[2]

They have been described as generally placid creatures, less so than B. gabonica, but not as bad-tempered as B. arietans. When approached, they often reveal their presence by hissing,^[2] said to be the loudest hiss of any African snake—almost a shriek.^[5]

Feeding

Preferring to hunt by ambush, it probably spends much of its life motionless, waiting for prey to wander by.^[5] Froesch (1967) described a captive specimen that would hardly ever leave its hide box, even when hungry, and once waited for three days for a live mouse to enter its hide box before striking. Feeding mainly on small mammals, but in wetland habitats, it is also known to take toads, frogs and even fish. One long-term captive specimen, regularly fed killed mice and frogs, always held on to its prey for several minutes after a strike before swallowing.^[2]

Reproduction

In West Africa, the species gives birth to between six and 38 young in March-April at the beginning of the rainy season. Neonates are 18–25 cm in length.^[5] In eastern Africa, the breeding season is indefinite.^[3]

Venom

Because of its restricted range, few bites have been reported. No statistics are available.^[3]

Relatively little is known about the toxicity and composition of the venom. In mice, the intravenous LD₅₀ is 1.1 mg/kg. The venom is supposedly slightly less toxic than those of B. arietans and B. gabonica. The maximum wet venom yield is 200 mg.^[3] One study reported this venom has the highest intramuscular LD₅₀ value—8.6 mg/kg—of five different viperid venoms tested (B. arietans, B. gabonica, B. nasicornis, Daboia russelii and Vipera aspis). Another showed little variation in the venom potency of these snakes, whether they were milked once every two days or once every three weeks. In rabbits, the venom is apparently slightly more toxic than that of B. gabonica.^[2]

In only a few detailed reports of human envenomation, massive swelling, which may lead to necrosis, had been described.^[3] In 2003, a man in Dayton, Ohio, who was keeping a specimen as a pet, was bitten and subsequently died.^[9] At least one antivenin protects specifically against bites from this species: India Antiserum Africa Polyvalent.^[10]

See also

• List of viperine species and subspecies
• Viperinae by common name
• Viperinae by taxonomic synonyms
• Snakebite

References

Further reading